1. Field of the Invention
The present disclosure relates to LED backlight driving circuit technology, and more particularly to a LED backlight driving circuit capable of precisely adjusting the current of LED units, and the liquid crystal device with the same.
2. Discussion of the Related Art
With the technical evolution, the backlight technology for the LCDs has been developed. In the past, CCFLs are adopted as backlight sources. However, LEDs have now been adopted as backlight sources for the reason that the CCFLs have the disadvantages, such as low color restoration, low lighting efficiency, high discharging voltage, bad discharging characteristics at low temperature, and long heating time to achieve stable gray level. Generally, the LED backlight source is arranged opposite to the liquid crystal panel so as to provide the light source to the liquid crystal panel. The LED backlight source includes at least one LED string having a plurality of serially connected LEDs.
FIG. 1 is a schematic view of a typical driving circuit of LED backlight source for liquid crystal devices. As shown, the LED backlight driving circuit includes a driving module for providing a driving voltage to a LED unit 2. The driving module 1 receives a control voltage received from a voltage control module 3 for controlling the driving voltage. At the same time, a feedback voltage module 4 is provided between the LED unit 2 and the ground. The feedback voltage module 4 generates a feedback voltage to the driving module 1. The driving module 1 monitors a current amount of the LED unit 2 by monitoring the value of the feedback voltage. The driving module 1 is capable of adjusting the value of the driving voltage according to the value of the feedback voltage so as to change the value of the driving voltage. In order to obtain stable light source in the LED backlight driving circuit, the driving current has to be precise enough. As stated, referring to circuit shown in FIG. 1, the driving current is configured according to the control voltage of the voltage control module 3 and the feedback voltage of the feedback voltage module 4. FIG. 2 is a circuit diagram of the voltage control module 3. The control voltage (Vd) is obtained by diving the voltage (Vcc) by resistance voltage dividers (Rc1, Rc2). The deviation of the resistance voltage dividers (Rc1, Rc2) may affect the control voltage (Vd), and so as the precision of the driving current. FIG. 3 is a circuit diagram of the feedback voltage module 4. The drain of the first MOS transistor Q1 connects to the negative end of the LED unit 2. The gate (G) of the first MOS transistor Q1 is controlled by the driving module 1. The source of the first MOS transistor Q1 is grounded via a feedback resistor (Rs). The feedback voltage (Vs) obtained from the feedback resistor (Rs) is inputted to the driving module 1. By monitoring the value of the feedback voltage (Vs), the amount of the current of the LED unit 2 is monitored so as to obtain an appropriate current value by adjustment. Within the circuit, the two parameters, i.e., control voltage (Vd) and feedback voltage (Vs), of the driving current are obtained by the resistance voltage dividers. The deviation of the resistance voltage dividers results in the deviation of the control voltage (Vd) and the feedback voltage (Vs). As such, the precision of the driving current is also affected.